Exhaust pipe joint structure and coil spring used in the same

ABSTRACT

An automobile exhaust-pipe joint structure and a coil spring for use therein. The exhaust pipe connection structure includes a first exhaust pipe having a first flange section, a second exhaust pipe having a second flange section, a ball joint section for connecting the first and second exhaust pipes flexibly, and coupling mechanisms provided at a plurality of positions of the first and second flange sections. One exemplary coupling mechanism includes a bolt member penetrating the first flange section and being secured, at one end part thereof, to the second flange section, and a coil spring of deformed cross-section interposed between the other end part of the bolt member and the first flange section, wherein the cross-section of a wire is reduced in diameter, in the compressing direction with a dimensional ratio between the short diameter and long diameter thereof being in the range of 1.1–2.6.

TECHNICAL FIELD

The present invention relates to a joint structure using a ball jointfor an automobile exhaust pipe and to a coil spring used in the same.

BACKGROUND ART

Ball joints have been used as vibration isolation joints in anautomobile exhaust line. They absorb the vibration of a car body toprevent an excessive stress from acting on an engine exhaust section andan exhaust-pipe joint section.

Various specific joint structures have been proposed and put in actualuse. For example, there are joint structures described in JP-A-10-176777and JP-UM-T-2598461.

A typical structure will be described with reference to FIG. 6.

An exhaust pipe is composed of a first exhaust pipe 1 and a secondexhaust pipe 2. The exhaust pipes 1 and 2 are flexibly joined togetherwith a ball joint mechanism B.

The first exhaust pipe 1 guides exhaust gas from an automobile engine tothe second exhaust pipe. The first exhaust pipe 1 is called an exhaustmanifold. The second exhaust pipe 2 discharges the exhaust gas into theatmosphere.

More specifically, the joint section between the first exhaust pipe 1and the second exhaust pipe 2 has a ball section 3 shaped like a ball inexternal form adjacent to the second exhaust pipe 2, and has a flaresection 5 near the first exhaust pipe 1. The flare section 5 has aninner curve 4 corresponding to the ball section 3.

The first exhaust pipe 1 and the second exhaust pipe 2 have a firstflange section la and a second flange section 2 a, respectively. Thefirst flange section 1 a and the second flange section 2 a have opposedsurfaces, respectively. The flange sections 1 a and 2 a have openings 1b and 2 b at opposed positions so that a bolt 8 (described later) ispassed through. The flange sections 1 a and 2 a are fixed to each otherwith joint mechanisms C.

The joint mechanisms C are provided at a plurality of positions of thefirst and second flange sections to join the first and second flangesections together.

One of the joint mechanisms C has a nut 7, the bolt 8, and a coil spring20. The nut 7 is fixed to the periphery of the opening 2 b of the secondflange section 2 a by welding 9.

The bolt 8 passes through the respective openings 1 b and 2 b of theflange sections 1 a and 2 a. One end 8 a of the bolt 8 is screwed andsecured in the nut 7. The bolt 8 is passed through the center of thewinding coil spring 20.

The coil spring 20 is arranged between the other end (i.e., head) 8 b ofthe bolt 8 and the first flange section 1 a. The coil spring 20 pushesthe first exhaust pipe 1 through the first flange section 1 a toward thesecond exhaust pipe 2.

When a bending force is applied between the first exhaust pipe 1 and thesecond exhaust pipe 2 by the vibration of the car body, the ball section3 slides in the inner curve 4 of the flare section 5 to allow the firstexhaust pipe 1 and the second exhaust pipe 2 to curve. The coil spring20 keeps the close contact between the ball section 3 and the innercurve 4 to prevent leakage of exhaust gas.

In such an exhaust-pipe joint structure, the coil spring 20 is formed bywinding a circular-section wire rod in coiled form. The height of thecoil spring 20 is given by n×d when compressed until the wire rodsconstituting the coil spring 20 come into contact with each other, whered is the diameter of the wire rod and n is the number of turns of thecoil spring.

Accordingly, the length of part of the bolt 8 which is passed throughthe coil spring inevitably must be longer than n×d. This increases thefull length of the bolt 8, thus increasing the weight relatively.

Also, because the coil spring is high, the lateral movement increaseswhen a bending stress is applied in use. Also, there is the problem ofincreasing the contact between the wire rods of the coil spring toincrease the moment.

On the other hand, it is the most important object to improve the fuelefficiency of cars in view of recent environmental issues. To this end,automobile makers have been making various improvements includingdevelopment of high-efficiency engines, improvement in a combustionmethod, improvement in fuel quality, development of new driving sourcessuch as fuel cells. On the other hand, it is well known that continuousefforts have been made to improve fuel efficiency by weight reduction ofcar bodies.

In order to reduce the weight of car bodies, strenuous efforts have beenmade from the weight reduction of car body structures to the weightreduction of various components in grams.

Also the exhaust pipe system that is the subject of the presentinvention intends to make the exhaust pipe thinner and to make the bolt8 of the joint mechanism C smaller in diameter. Although it is said thatthe weight reduction is recently at its limit, further weight reductionis required for the Earth's environment.

The present invention has been made in consideration of the presentsituation. Accordingly, it is a first object of the invention to providea coil spring capable of further weight reduction of an exhaust-pipejoint structure and a new exhaust-pipe joint structure using the coilspring. Furthermore, a second object is to provide a coil spring capableof cost reduction of an exhaust-pipe joint structure and a newexhaust-pipe joint structure using the coil spring.

DISCLOSURE OF THE INVENTION

The present invention has been made, focusing on improvements in thestructure of a coil spring, to which no attention has been paid in theconventional weight reduction measures.

In order to achieve the above objects, the coil spring according to theinvention is formed of the following wire rod that is wound in coiledshape. The cross section of the wire rod of the coil spring is adeformed cross section having a minor axis and a major axis such that itis small in diameter in the direction in which the coil spring iscompressed. The dimension ratio of the major axis to the minor axis iswithin the range from 1.1 to 2.6.

The automobile exhaust-pipe joint structure according to the inventionis an exhaust-pipe joint structure that uses the coil spring of theinvention in order to achieve the above objects.

The automobile exhaust-pipe joint structure includes a first exhaustpipe having a first flange section at one end; a second exhaust pipehaving a second flange section at one end; a ball joint mechanismdisposed at the ends at which the first flange section of the firstexhaust pipe and the second flange section of the second exhaust pipeare formed to flexibly join the first exhaust pipe and the secondexhaust pipe together; and joint mechanisms disposed in a plurality ofpositions of the first flange section and the second flange section, forjoining the first flange section and the second flange section together.

One of the joint mechanisms includes a bolt one end of which is fixed tothe second flange section through the first flange section; and a coilspring arranged between the other end of the bolt and the first flangesection, the joint mechanism using as the coil spring theabove-described coil spring of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of an essential part of an exhaust-pipe jointstructure according to an embodiment of the present invention;

FIG. 2 is a sectional view of a coil of a coil spring of FIG. 1;

FIG. 3 is a side view of a coil spring formed by winding theflat-section wire rod of FIG. 2 in coiled form;

FIGS. 4( a), 4(b), 5(a), and 5(b) are graphs that compares thecharacteristics of the coil of the invention with those of aconventional coil spring; and

FIG. 6 is a sectional view of an essential part of one example of aconventional exhaust-pipe joint structure.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring to FIGS. 1 to 5( b), an embodiment of the present inventionwill be described hereinafter. Components that function as in those ofFIG. 6 are given by the same reference numerals and a descriptionthereof will be omitted. Referring to FIG. 1, a part different from FIG.6 is a coil spring. In FIG. 1, numeral 6 denotes a coil spring.

The automotive exhaust-pipe joint structure of the present invention isan exhaust-pipe joint structure that uses a coil spring according to theinvention.

In the embodiments, the coil spring 6 of the invention is formed bywinding a wire rod in coil form, as shown in FIG. 1. The wire rod isdeformed in cross section such that it is small in diameter in thedirection A in which the coil spring 6 is compressed and long indiameter in the direction crossing the direction A in which the coilspring 6 is compressed.

More specifically, referring to FIG. 2, the deformed cross section ofthe wire rod is a flat cross section having two straight lines 6 cextending along the major axis in parallel. The straight lines 6 c areformed to cross the direction A in which the coil spring 6 iscompressed. The straight lines 6 c in the cross section extend along themajor axis of the wire rod to form a planar surface 6 e of the wire rod(refer to FIG. 3).

Furthermore, the deformed cross section of the wire rod has two circulararcs 6 d. The two circular arcs 6 d are located between the straightlines 6 c to connect the respective ends of the straight lines 6 ctogether. Both of the circular arcs 6 d are curved to project from thestraight lines 6 c.

The ratio of a major axis d1 to a minor axis d2 (d1/d2) is preferablyset within the range from 1.1 to 2.6. When the ratio is smaller than1.1, there is no difference in effect from the conventionalcircular-section wire rod. When the ratio exceeds 2.6, the cross sectionof the wire rod comes into a nearly plate shape to decrease the springconstant. Therefore, the number of turns of the coil spring must beincreased, thus posing the problem of increasing the height of the coilspring. It is most preferable to set the ratio of the major axis d1 tothe minor axis d2 (d1/d2) within the range from 1.3 to 2.0.

The method of making the wire rod of the coil spring 6 includes thefollowing: a method of passing the conventionally-used circular-sectionwire rod between a pair of upper and lower reduction rollers to coldroll it or a method of cold drawing the circular-section wire rod.

The cold rolling or the cold drawing increases the hardness of the wirerod. Therefore, the strength, fatigue characteristics, and thecharacteristic against permanent set are increased. This provideslow-cost high-quality wire rods.

Also, this provides wire rods finer than the conventional ones, so thatit is to be expected that the coil spring will be decreased in weight.

The dimension ratio (d3/d1) of the length d3 of the straight lines 6 cof the cross section (the width of the planar surface 6 e) to the majoraxis d1 is preferably set within the range from 0.4 to 0.9. When thevalue is smaller than 0.4, sufficient effects flatness and of coldworking cannot be provided. When the value is larger than 0.9, theflatness becomes excessive so that the coil spring 6 becomes a nearlyplate shape, which may produce the problem of an improper springconstant. The ratio of the length of the straight lines 6 c (i.e., thewidth of the planar surface) to the major axis d1 is more preferablywithin the range from 0.5 to 0.8.

When the cross section of the wire rod is flat shaped, the height of thecoil spring in a state in which it is compressed to come into contactwith each other (i.e., closed height) is smaller than that of theconventional coil springs with the circular-section wire rod.

Particularly, setting the ratio of the major axis to the minor axis inthe above-described predetermined range allows the closed height to bedecreased as much as a maximum of 60 percent.

Consequently, even with a coil spring having the same spring constant asthat of the conventional ones, the height of the uncompressed coilspring (i.e., free height) can be decreased. Therefore, the length ofthe bolt 8 used in combination with the coil spring can also bedecreased. This can significantly decrease the weight of the coil spring6 and the bolt 8 that form the joint mechanism C.

Particularly, the optimal design allows the total weight of the bolt andthe coil spring to be reduced to about 50 percent of the conventionalones. It is to be expected that it will contribute to an improvement infuel efficiency owing to the weight reduction of cars and toimprovements in the problems of the Earth's environment including theproblem of carbon dioxide.

When the displacement angles of the ball-joint section are the same, thefree height decreases, so that the lateral movement of the coil springis decreased. Accordingly, the contact of the wire rods of the coil isalso decreased; thus, also the moment becomes smaller than that of theconventional ones at the same displacement angle. As a result, thevibration isolation performance of the ball joint section will beimproved.

A significant decrease in the closed height of the coil spring increasesthe flexibility in selecting the dimensions of the material. This allowsa compact and smart design of the coil spring and improves thein-vehicle mounting performance of the exhaust-pipe joint structure.

Referring to FIG. 3, at opposite ends 6 a and 6 b of the coil spring 6,flat bearing surfaces are formed to mount the coil. The bearing surfacesof the coil spring are formed by using the planar surfaces 6 e of thewire rod of the coil spring.

More specifically, a starting end 6 a of the coil spring 6 is wound toform the bearing surface for the coil such that at least 50 percent to100 percent, preferably 80 percent to 100 percent, of the length of oneturn at the starting end is in an assumed surface S1. Similarly, aterminal 6 b of the coil spring 6 is wound to form the bearing surfacefor the coil such that at least 50 percent to 100 percent, preferably 80percent to 100 percent, of the length of one turn at the terminal is inan assumed surface S2.

The member to which the coil spring is mounted has a planar mountingsurface for the coil spring. The assumed surfaces S1 and S2 planes areassumed as the mounting surfaces.

At the opposite ends 6 a and 6 b of the coil spring 6, it is the planarsurfaces 6 e of the coil-spring wire rod that are substantially in theassumed surfaces S1 and S2.

Accordingly, it becomes unnecessary to grind the bearing surface of thecoil spring, which was necessary for the conventional circular-sectionwire rods, resulting in simplification of the coil spring productionprocess and the reduction of production cost.

When the conventional circular-section wire rod is used, the oppositeends of the coil spring were ground into a planar surface to form aplanar bearing surface for the coil spring. Therefore, according to theinvention, no chips generate, thus contributing to the reduction ofwastes in production process.

[Test]

The moment that acts on the bolt was measured. The coil springs used inthe measurement were made as follows:

EXAMPLE

A circular-section SUS316N wire rod (3.2 mm in diameter) was prepared.The wire rod was cold rolled to form a flat-section wire rod. The flatsection measured as follows:

Major axis (d1)=3.52 mm; minor axis (d2)=2.55 mm; the ratio of majoraxis to minor axis (d1/d2)=1.38; width of planar surface (d3)=1.8 mm;and the ratio of width of planar surface to major axis (d3/d1)=0.51.

A coil spring was made of the flat-section wire rod. The specificationsof the coil spring were as follows:

Outside diameter=24 mm; total number of turns=4.5 (the number of activeturns=3, the number of turns at opposite bearing surfaces=0.75); freeheight=30.5 mm; closed height=14.5 mm; and spring constant=29.4 N/mm (3kgf/mm).

COMPARATIVE EXAMPLE

A coil spring was made of a circular-section SUS316N wire rod (3.2 mm indiameter) as a comparative example. The specifications of the coilspring were as follows:

The same spring constant as the coil spring of the above example [springconstant=29.4 N/mm (3 kgf/mm)]; total number of turns=7.5 (the number ofactive turns=5.5; the number of turns at opposite surfaces=1.0); andfree height=42.0 mm.

The measurement was conducted as follows:

As FIG. 1 shows, the automotive exhaust-pipe joint structure wasconnected with the above coil spring. The coil spring and the bolt wereused in the periphery of the exhaust pipe, two positions at 0° and 180°.

The moment that acts on the bolt was measured while a bending stress wasapplied to the ball joint section. The direction in which the bendingstress is applied included the following four-directions:

Direction 1:

The coil-spring-winding start position was set in the 12 o'clockposition, seen from the position of applying a displacement stress.

Direction 2:

The coil-spring-winding start position was set in the 3 o'clockposition, seen from the position of applying a displacement stress.

Direction 3:

The coil-spring-winding start position was set in the 6 o'clockposition, seen from the position of applying a displacement stress.

Direction 4:

The coil-spring winding start position was set in the 9 o'clockposition, seen from the position of applying a displacement stress.

The measurements are shown in the graphs of FIGS. 4( a), 4(b), 5(a), and5(b). The graphs plot the relationship between the displacement angle(deg) of the ball joint section and the moment applied to the bolt (Nm).A rhomb-shaped mark in the graphs indicates the example and a filled-dotmark denotes the comparative example.

Referring to FIG. 4( a), the direction in which the bending stress actsis direction 1. Referring to FIG. 4( b), the direction in which thebending stress acts is direction 2. Referring to FIG. 5( a), thedirection in which the bending stress acts is direction 3. Referring toFIG. 5( b), the direction in which the bending stress acts is direction4.

(Consideration)

As the graphs clearly show, the example shows a lower moment than thatof the comparative example in any directions in the same displacementangle. This shows that the vibration isolation performance of the jointsection has been improved.

The result was probably obtained as follows:

The coil spring of the example can be lower in closed height than thatof the comparative example. Therefore, in this example, also the freeheight of the coil spring could be set low, so that the bolt could alsobe shorter.

As a result, the lateral movement of the coil spring was decreased atthe same displacement angle and the moment relative to displacementangle (i.e., oscillating torque) was also decreased.

While the preferred embodiment of the present invention has beendescribed, it is to be understood that the invention is not limited tothat and various modifications may be made without departing from thesprit and scope of the invention.

INDUSTRIAL APPLICABILITY

The coil spring according to the invention is most suitable as a coilspring capable of weight reduction and cost reduction of an automobileexhaust-pipe joint structure.

Furthermore, the automobile exhaust-pipe joint structure of theinvention is most suitable as a joint structure capable of furtherweight reduction and cost reduction by using the coil spring accordingto the invention.

1. an automobile exhaust-pipe joint structure, comprising: a firstexhaust pipe having a first flange section at one end; a second exhaustpipe having a second flange section at one end; a ball joint mechanismdisposed at the ends where the first flange section of the first exhaustpipe and the second flange section of the second exhaust pipe are formedto flexibly join the first exhaust pipe and the second exhaust pipetogether; and joint mechanisms disposed in a plurality of positions atthe first flange section and the second flange section, for joining thefirst flange section and the section flange section together; whereinone of the joint mechanisms includes: a bolt, one end of which is fixedto the second flange section through the first flange section; and acoil spring disposed between the other end of the bolt and the firstflange section; wherein the cross section of the wire rod of the coilspring is a deformed cross section having a minor axis and a major axissuch that it is small in diameter in the direction in which the coilspring is compressed, the dimension ratio of the major axis to the minoraxis being within the range from 1.1 to 2.6.
 2. An automobileexhaust-pipe joint structure according to claim 1, wherein the dimensionratio of the major axis to the minor axis is within the range from 1.3to 2.0.
 3. An automobile exhaust-pipe joint structure according to claim1, wherein the cross section of the wire rod of the coil spring includestwo straight lines extending along the major axis in parallel and twocircular arcs located between both the straight lines to connect therespective ends of the straight lines together, both the circular arcsbeing curved to project from the straight lines; wherein the dimensionratio of the length of the straight lines to the major axis is withinthe range from 0.4 to 0.9.
 4. An automobile exhaust-pipe joint structureaccording to claim 3, wherein the dimension ratio of the length of thestraight lines to the major axis is within the range from 0.5 to 0.8. 5.An automobile exhaust-pipe joint structure according to claim 1, whereinthe wire rod of the coil spring is a circular-section wire rod subjectedto cold rolling or cold drawing so that the cross section has a majoraxis and a minor axis.
 6. An automobile exhaust-pipe joint structureaccording to claim 1, wherein the cross section of the wire rod of thecoil spring has two straight lines extending in parallel in thedirection to cross the direction of compression of the coil spring; thewire rod of the coil spring has planar surfaces formed by the straightlines in the cross section extending along the length of the wire rod; astarting end of the coil spring formed of the wire rod having the planarsurfaces is wound to form a bearing surface for the coil such that atleast from 50 percent to 100 percent of the length of one turn at thestarting end is in an assumed surface; and a terminal of the coil springis similarly wound to form a bearing surface for the coil such that atleast from 50 percent to 100 percent of the length of one turn at theterminal is in another assumed surface.
 7. An automobile exhaust-pipejoint structure according to claim 6, wherein the starting end of thecoil spring formed by the wire rod having the planar surfaces is woundto form a bearing surface for the coil such that at least from 80percent to 100 percent of the length of one turn at the starting end isin an assumed surface; and the terminal of the coil spring is similarlywound to form a bearing surface for the coil such that at least from 80percent to 100 percent of the length of one turn at the terminal is inanother assumed surface.
 8. A coil spring used as a coil spring in anautomobile exhaust-pipe joint structure, wherein the automobileexhaust-pipe joint structure comprises a first exhaust pipe having afirst flange section at one end; a second exhaust pipe having a secondflange section at one end; a ball joint mechanism disposed at the endswhere the first flange section of the first exhaust pipe and the secondflange section of the second exhaust pipe are formed to flexibly jointhe first exhaust pipe and the second exhaust pipe together; and jointmechanisms disposed in a plurality of positions at the first flangesection and the second flange section, for joining the first flangesection and the second flange section together; wherein one of the jointmechanisms includes: a bolt, one end of which is fixed to the secondflange section through the first flange section; and a coil springarranged between the other end of the bolt and the first flange section;wherein the coil spring is formed by winding a wire rod in coiled form;and the cross section of the wire rod of the coil spring is a deformedcross section having a minor axis and a major axis such that it is smallin diameter in the direction in which the coil spring is compressed, thedimension ratio of the major axis to the minor axis being within therange from 1.1 to 2.6.
 9. A coil spring according to claim 8, whereinthe dimension ratio of the major axis to the minor axis is within therange from 1.3 to 2.0.
 10. A coil spring according to claim 8, whereinthe cross section of the wire rod of the coil spring includes twostraight lines extending along the major axis in parallel; and twocircular arcs located between both the straight lines to connect therespective ends of the straight lines together, the circular arcs beingcurved to project from the straight lines; wherein the dimension ratioof the length of the straight lines to the major axis is within therange from 0.4 to 0.9.
 11. A coil spring according to claim 10, whereinthe dimension ratio of the length of the straight lines to the majoraxis is within the range from 0.5 to 0.8.
 12. A coil spring according toclaim 8, wherein the wire rod of the coil spring is a circular-sectionwire rod subjected to cold rolling or cold drawing so that the crosssection has a major axis and a minor axis.
 13. A coil spring accordingto claim 8, wherein the cross section of the wire rod of the coil springhas two straight lines extending in parallel in the direction to crossthe direction of compression of the coil spring; the wire rod of thecoil spring has planar surfaces formed by the straight lines in thecross section extending along the length of the wire rod; a starting endof the coil spring formed by the wire rod having the planar surfaces iswound to form a bearing surface for the coil such that at least from 50percent to 100 percent of the length of one turn at the starting end isin an assumed surface; and a terminal of the coil spring is similarlywound to form a bearing surface for the coil such that at least from 50percent to 100 percent of the length of one turn at the terminal is inanother assumed surface.
 14. A coil spring according to claim 13,wherein the starting end of the coil spring formed by the wire rodhaving the planar surfaces is wound to form a bearing surface for thecoil such that at least from 80 to 100 percent of the length of one turnat the starting end is in an assumed surface; and the terminal of thecoil spring is similarly wound to form a bearing surface for the coilsuch that at least from 80 percent to 100 percent of the length of oneturn at the terminal is in another assumed surface.